1. Field of the Invention
The present invention relates to a device used in printers for compressing paper using clamshell-type during a printing process and, more particularly, to a clamshell device for printers having a simple construction and accomplishing the recent trend of compactness, lightness, smallness and thinness of its parts, thus being preferably usable in compact printers, the clamshell device being also designed to improve work efficiency during its fabrication and effectively produced through mass production.
2. Description of the Prior Art
FIG. 1 is a view showing a conventional clamshell device for printers. As shown in the drawing, the conventional clamshell device comprises a cover 11, which is hinged to a main body (not shown) at one end thereof so as to be openable. A rubber roller 14 mounted to the roller frame 12, which is hinged to the cover 11, rotate itself and compresses the paper to be fed to a printer head while maintaining desired tension of the paper during a printing process. A sliding frame 13 hinged to the main body use the elastic force of spring 13xe2x80x2, which is normally connected to the main body, so as to support the roller frame 12. A locking member 16 is hinged to the end of the cover 11, and is selectively caught by a stopper 17 of the main body, thus limiting a rotation of the cover 11. A holding roller 15 is mounted to the main body and comes into close contact with the rubber roller 14 so as to support the paper, which is moving into the printer head (not shown) during a printing process of the printer.
In the conventional clamshell device, the rubber roller 14 and the holding roller 15 are completely contact each other during a printing process, thus give a compressing force to the paper passing through the nip between the two rollers.
When the cover 11 is rotated in a cover closing direction as shown by the arrow in FIG. 1, the roller frame 12 hinged to the cover 11 is also rotated in the same direction. The rubber roller 14, mounted to the end of the roller frame 12, is brought into compression contact with the holding roller 15 of the main body, thus compressing the paper fed to the printer head of the printer. Therefore, the paper is fed to the printer head under sufficient tension during a printing process.
In order to maintain the closed position of the cover 11, it is necessary for the stopper 17 to stably catch the locking member 16 provided at the end of the cover 11. When the stopper 17 fails to catch the locking member 16 during such a cover closing action, the roller frame 12 is undesirably rotated clockwise since the spring 13xe2x80x2 normally applies the clockwise moment to the sliding frame 13. In such a case, it is almost impossible to maintain the compression contact of the rubber roller 14 with the holding roller 15. When the rubber roller 14 fails to come into compression contact with the holding roller 15 as described above, the two rollers 14 and 15 cannot compress the paper and fail to smoothly feed the paper to the printer head of the printer.
This means that the compression force, applied to the paper during an operation of the clamshell device for printers, is accomplished by the engagement of the locking member 16 of the cover 11 with the stopper 17 of the main body. In addition, the spring 13xe2x80x2 applies elastic force to the sliding frame 13 so as to damp any impact generated in the clamshell device during a cover opening or closing action.
However, the conventional clamshell device for printers is problematic in that for making complete compression contact between the rubber roller and the holding roller, it is necessary a locking structure additionally. Other problems of the conventional clamshell device reside in that the device does not have any automatic tilting means, and that it has a complex construction, in addition to an excessive number of parts. Furthermore, the parts of the conventional clamshell device for printers are large in size, and so the conventional clamshell device cannot be usable in compact and small-sized printers.
The object of the present invention is to provide a clamshell device for printers, which has a simple construction and accomplishes the recent trend of compactness, lightness, smallness and thinness of its parts, thus improving work efficiency during assemblage and being easily produced in commercial quantities.
In order to accomplish the above object, the present invention provides a clamshell device for printers, comprising: a main body including a paper roll seat opening used for installing a paper roll therein, with a guide surface, which is formed at the upper edge of each sidewall, inclined at an angle of inclination; a roller frame hinged to the main body and closing the paper roll seat opening, the roller frame having a holding roller coming into compression contact with a rubber roller of the main body so as to give compression force to paper passing through the nip of the rubber and holding rollers; a locking post movably set within two longitudinal slits of the roller frame at its side wall, said locking post being movable along the guide surfaces of the main body while being changed in its position within the longitudinal slits during an either directional rotation of the roller frame relative to the main body; and a spring held on the roller frame at one end thereof and on the main body at the other end thereof, and normally applying elastic force to the roller frame.
In this invention, a stopper is formed on the main body for preventing an excessive rotation of the roller frame.
In addition, the guide surfaces has a shoulder profile capable of stably holding the locking post in cooperation with the elastic force of the spring at a time the holding roller of the roller frame comes into compression contact with the rubber roller of the main body.
In the preferred embodiment of this invention, the spring is held by the locking post of the roller frame at one end thereof and by a spring holding shaft at the other end thereof, the spring holding shaft being provided around the bottom of the paper roll seat opening.